Air-to-water heat pumps: the next frontier

By Michael Ridler

This, is quite frankly, a very exciting time to be the air-to-water Heat Pump game. There is a slew of players that have entered the market or looking to in the coming years.

I am a huge fan of air-to-water and ground-source heat pumps, with each type of technology serving its niche in the market. There is no question that a ground-source heat pump is the most efficient way to heat and cool homes. But you can’t dismiss the value of what I affectionately refer to as the “baby brother” of ground-source heat pumps, which is the air-to-water heat pump.

Some people still look at air-to-water as the future of boilers, and I don’t disagree, but I also think it is more important to realize that heat pumps are not boilers, and we don’t design them the same. Frankly, they do much more than a boiler or an air-to-air heat pump.

Why air-to-water
Air-to-water offers a level of versatility that is only beat by a ground-source heat pump. Air-to-water heat pumps can be used to heat radiant floor systems, which can be more energy efficient and provide more comfortable heat compared to a forced air system. It can also be used to heat domestic hot water, providing a dual function that an air-source heat pump can’t.

An air-to-water system can also operate at lower temperatures compared to an air-to-air system, which can make it more energy efficient, especially when used with underfloor heating systems. As a result, air-to-water heat pumps often have a higher COP compared to air-to-air systems, making them more efficient in converting energy into heat. It can also provide more even heat distribution compared to forced-air systems.

The first thing we are starting to see is manufacturers designing and developing indoor modular units that take all the guesswork out of the installation. Most of these units are monobloc with the compressor outside, and water and glycol moving from outside to an engineered indoor module.

Usually, it is an issue with cooling not working properly or the domestic hot water not keeping up. When we pipe air-to-water equipment, we need to think about how we are handling the cooling. We also have to recognize that although an air-to-water heat pump can heat your hot water, it is not like a boiler.

This is where the advent of modular indoor units is so important. For example, take a look at the following photo.

Lego mechanical rooms
This is where the advent of modular indoor units is so incredibly important. Packaged indoor units can be engineered to provide heating, cooling, domestic hot water, defrost controls, and backup heat. Some would look at this type of system, see the price tag, and run in the opposite direction.

Indoor units like the one shown save you hours and ensure the systems work. You don’t have to worry about anything other than connecting to the outdoor unit and connecting your loads to the outlets of the indoor box.
The labour component of any job is often the most variable and can significantly impact the outcome of a project, explains Mike Miller, vice president of sales for Canada at Taco Comfort Solutions. There are numerous factors to consider when installing an air-to-water heat pump, including the integration of major components like the use of isolation relays, control strategies, sensor placement, system wiring, and the often-underestimated smaller components.

An indoor unit can simplify this complexity, offering a solution that standardizes every system, encloses it within a single unit, and essentially turns it into a plug-and-play appliance. This approach not only streamlines support, service, and troubleshooting but also saves valuable time that can be better invested in other endeavours.

Hybrid heating controls
Right now, there are a few controls on the market that can be used for your air-to-water applications especially if they are heating-only or cooling-only (i.e., no auto changeover).

Innovative control systems serve as an ideal middle ground for individuals who are confident in their ability to handle the intricacies of piping and engineering indoor secondary systems for air-to-water heat pumps. However, it’s crucial to heed the wisdom of those more experienced in the field. If you don’t understand hydronic heat pumps, seek out advice.

If you are doing a single air-to-water system, the modular indoor/outdoor works beautifully. If you are doing multiple air-to-water units, the stand-alone control is quite frankly, a complete no-brainer.

Game-changing technology
Phase change media technology emerges as a game-changer, especially in the realm of air-to-water heat pumps. I have worked with many engineers over the years on thermal storage projects from residential to agricultural, and they offer some challenges that are quickly being defeated by the advent of phase change batteries. This innovative technology leverages phase change materials to store heat more densely compared to water, effectively reducing the size of the storage tanks needed.

“Phase change thermal storage is an exciting technology because of the benefits it will provide to consumers, utilities, and governments alike,” according to Stephen Harrison, professor of mechanical and materials engineering at Queen’s University. “By improving storage efficiency and reducing the size of storage required, phase change thermal storage will revolutionize domestic water and space heating while improving utilities’ abilities to shift peak loads. There is still work to be done to bring this technology to full market, but change is coming quickly.”

Phase change materials are typically made from a variety of materials including salt hydrates, fatty acids, or paraffins, among others. These materials are chosen based on their ability to store and release heat effectively through phase changes, which occur at predetermined temperatures. They can also be used for cooling and domestic hot water.

The technology ensures a more consistent and efficient release of heat, enhancing the performance of air-to-water heat pumps significantly.

It also curtails energy losses, which are common in water-based systems. This is not technology we will be waiting long to see.

Dual-source heat pumps
The dual-source heat pump stands as a groundbreaking advancement because it combines an air-to-water heat pump with a ground-source heat pump. It is specifically designed for locations with limited ground space. This system operates either as an air-to-water heat pump using air as a source/sink or as a brine-to-water heat pump coupled to the ground. It is designed as an outdoor plug-and-play unit, working with R32 refrigerant and including a variable speed compressor, which allows for efficient modulating operation.

A significant advantage of the dual-source heat pump system is its ability to minimize the footprint of the ground heat exchanger.

Incredibly, the dual-source heat pump system promises similar or even higher energy efficiency compared to ground-source heat pumps. It offers a variety of operating modes, including free-cooling conditions, and adapts to a wide range of thermal demands. It is suitable for many different applications, including small multifamily houses to offices.

Portable air-to-water window units
I have often wondered why there is no portable window air-to-water equipment for rental units. Recently, the B.C. government provided millions for rental units to install A/C units and there was significant backlash when heat pumps weren’t included.

This was when I came across an air-to-water window unit currently being developed. The product, aptly named “The Gradient,” stands out with its utilization of R32 refrigerant. It operates with a cooling capacity of 8,600 BTU/hr and a heating capacity that ranges between 3,000 to 8,000 BTU/hr. Impressively, the unit showcases a high energy efficiency rating, with a CEER of 10.8, highlighting its capability to cool spaces while maintaining low energy consumption.

Portable air-to-water units can be controlled via a mobile app, which supports scheduling features for convenience.